arXiv subjects

Jameel-Un Nabi

Publications and source records attributed to Jameel-Un Nabi.

At least 19 recordsLinked to original sources

arXiv2025

On the role of pairing correlations in calculation of \b{eta}-decay half-lives within QRPA formalism

In this paper we show that the proton-neutron residual interaction can play an important role in the reliability of calculated $β$-decay half-lives. It may also improve the prediction power of the quasiparticle random phase approximation (QRPA) model. We further demonstrate that a reasonable choice of the particle-particle (attractive) and particle-hole force (repulsive) parameters can result in calculated half-lives in very good comparison with the measured ones. Pairing gaps have affect on calculated half-lives which we explore in this paper. We present our half-lives calculation using the proton-neutron QRPA (pn-QRPA) model possessing a multi-shell single-particle deformed space including a schematic interaction for some medium mass neutron-deficient nuclei undergoing $β^{+}$/EC decay. Our study shows a better agreement with the available experimental data as compared to former calculations.

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arXiv2025

Gamow-Teller strength distributions and stellar weak-interaction rates for $^{76}$Ge and $^{82}$Se using the deformed pn-QRPA model

We calculate Gamow-Teller strength distributions for $ββ$-decay nuclei $^{76}$Ge and $^{82}$Se using the deformed pn-QRPA model. We use a deformed Nilsson basis and consider pairing correlations within the deformed BCS theory. Ground state correlations and two-particle and two-hole mixing states were included in our pn-QRPA model. Our calculated strength distributions were compared with experimental data and previous calculation. The total Gamow-Teller strength and centroid placement calculated in our model compares well with the measured value. We calculate $β$-decay and positron capture rates on $^{76}$Ge and $^{82}$Se in supernovae environments and compare them to those obtained from experimental data and previous calculation. Our study shows that positron capture rates command the total weak rates at high stellar temperatures. We also calculate energy rates of $β$-delayed neutrons and their emission probabilities.

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arXiv2025

Unique first-forbidden $β$-decay transitions in odd-odd and even-even heavy nuclei

The allowed Gamow-Teller (GT) transitions are the most common weak nuclear processes of spin-isospin $(στ)$ type. These transitions play a key role in numerous processes in the domain of nuclear physics. Equally important is their contribution in astrophysics, particularly in nuclear synthesis and supernova-explosions. In situations where allowed GT transitions are not favored, first-forbidden transitions become significant, specifically in medium heavy and heavy nuclei. For neutron-rich nuclei, first-forbidden transitions are favored mainly due to the phase-space amplification for these transitions. In this work we calculate the allowed GT as well as unique first-forbidden (U1F) $|Δ$J$|$ = 2 transitions strength in odd-odd and even-even nuclei in mass range $70\leq A \leq214$. Two different pn-QRPA models were used with a schematic separable interaction to calculate GT and U1F transitions. The inclusion of U1F strength improved the overall comparison of calculated terrestrial $β$-decay half-lives in both models. The \textit{ft} values and reduced transition probabilities for the $2^-\longleftrightarrow 0^+$ transitions were also calculated. We compared our calculations with the previously reported correlated RPA calculation and experimental results. Our calculations are in better agreement with measured data. For stellar applications we further calculated the allowed GT and U1F weak rates. These include $β^{\pm}$-decay rates and electron/positron capture rates of heavy nuclei in stellar matter. Our study shows that positron and electron capture rates command the total weak rates of these heavy nuclei at high stellar temperatures.

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arXiv2025

Temperature-dependent nuclear partition functions and abundances in stellar interior

We calculate temperature-dependent nuclear partition functions (TDNPFs) and nuclear abundances for $728$ nuclei assuming nuclear statistical equilibrium (NSE). The theories of stellar evolution support NSE. Discrete nuclear energy levels have been calculated \textit{microscopically}, using the pn-QRPA theory, up to an excitation energy of $10$ MeV in the calculation of TDNPFs. This feature of our paper distinguishes it from previous calculations. Experimental data is also incorporated wherever available to ensure reliability of our results. Beyond 10 MeV we employ simple Fermi gas model and perform integration over the nuclear level densities to approximate the TDNPFs. We calculate nuclidic abundances, using the Saha equation, as a function of three parameters: stellar density, stellar temperature and lepton-to-baryon content of stellar matter. All these physical parameters are considered to be extremely important in stellar interior. Results obtained in this paper show that the equilibrium configuration of nuclei remains unaltered by increasing stellar density (only calculated nuclear abundances increases by roughly same order of magnitude). Increasing the stellar temperature smooths the equilibrium configuration showing peaks at neutron-number magic nuclei.

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arXiv2025

Nuclear structure and weak rates of heavy waiting point nuclei under rp-process conditions

The structure and the weak interaction mediated rates of the heavy waiting point (WP) nuclei $^{80}$Zr, $^{84}$Mo, $^{88}$Ru, $^{92}$Pd and $^{96}$Cd along $N = Z$ line were studied within the interacting boson model-1 (\mbox{IBM-1}) and the proton-neutron quasi-particle random phase approximation (\mbox{pn-QRPA}). The energy levels of the $N$ = $Z$ WP nuclei were calculated by fitting the essential parameters of \mbox{IBM-1} Hamiltonian and their geometric shapes were predicted by plotting potential energy surfaces (PESs). Half-lives, continuum electron capture rates, positron decay rates, electron capture cross sections of WP nuclei, energy rates of $β$-delayed protons and their emission probabilities were later calculated using the \mbox{pn-QRPA}. The calculated Gamow-Teller strength distributions were compared with previous calculation. We present positron decay $\&$ continuum electron capture rates on these WP nuclei under $rp$-process conditions using the same model. For the $rp$-process conditions, the calculated total weak rates are twice the Skyrme HF+BCS+QRPA rates for $^{80}$Zr. For remaining nuclei the two calculations compare well. The electron capture rates are significant and compete well with the corresponding positron decay rates under $rp$-process conditions. The finding of the present study supports that electron capture rates form an integral part of the weak rates under $rp$-process conditions and has an important role for the nuclear model calculations.

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arXiv2025

Allowed and unique first-forbidden stellar electron emission rates of neutron-rich copper isotopes

The allowed charge-changing transitions are the most common weak interaction processes of spin-isospin form that play a crucial role in several nuclear/astrophysical processes. The first-forbidden (FF) transition becomes important, in the circumstances where allowed Gamow-Teller (GT) transitions are unfavored, specifically for neutron-rich nuclei due to phase space considerations. In this paper deformed proton-neutron quasi-particle random phase approximation (pn-QRPA) model is applied, for the first time, for the estimation of allowed GT and unique first-forbidden (U1F) transitions ($|Δ$J$|$ = 2) of neutron rich copper isotopes in mass range 72 $\leq$ A $\leq$ 82 under stellar conditions. We compared our computed terrestrial $β$-decay half-life values with previous calculations and experimental results. It was concluded that the pn-QRPA calculation is in good accordance with measured data. Our study suggests that the addition of rank (0 and 1) operators in FF transitions can further improve the comparison which remain unattended at this stage. The deformed pn-QRPA model was employed for the estimation of GT and U1F stellar electron emission ($β$$^{-}$-decay) rates over wide range of stellar temperature (0.01 GK -- 30 GK) and density (10 -- 10$^{11}$ g/cm$^{3}$) domains for astrophysical applications. Our study shows that, in high density and low temperature regions, the contribution of U1F rates to total electron emission rates of neutron-rich copper nuclei is negligible.

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arXiv2025

Gamow-Teller strength and lepton captures rates on 66-71Ni in stellar matter

Charge-changing transitions play a significant role in stellar weak-decay processes. The fate of the massive stars is decided by these weak-decay rates including lepton (positron and electron) captures rates, which play a consequential role in the dynamics of core collapse. As per previous simulation results, weak interaction rates on nickel isotopes have significant influence on the stellar core vis-$\grave{a}$-vis controlling the lepton content of stellar matter throughout the silicon shell burning phases of high mass stars up to the presupernova stages. In this paper we perform a microscopic calculation of Gamow-Teller charge-changing transitions, in the $β$-decay and electron capture directions, for neutron-rich nickel isotopes ($^{66-71}$Ni). We further compute the associated weak-decay rates for these selected nickel isotopes in stellar environment. The computations are accomplished by employing the deformed proton-neutron quasiparticle random phase approximation (pn-QRPA) model. A recent study showed that the deformed pn-QRPA theory is well suited for the estimation of Gamow-Teller transitions. The astral weak-decay rates are determined over densities in the range of 10 -- 10$^{11}$g/cm$^{3}$ and temperatures in the range of 0.01$\times$10$^{9}$ -- 30$\times$10$^{9}$K. The calculated lepton capture rates are compared with the previous calculation of Pruet and Fuller. The overall comparison demonstrates that, at low stellar densities and high temperatures, our electron captures rates are bigger by as much as two orders of magnitude. Our results show that, at higher temperatures, the lepton capture rates are the dominant mode for the stellar weak rates and the corresponding lepton emission rates may be neglected.

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arXiv2025

Study of electron capture rates on chromium isotopes for core-collapse simulations

Electron capture rates on \emph{fp}-shell nuclei play a pivotal role in the dynamics of stellar evolution and core collapse. These rates play a crucial role in the gravitational collapse of the core of a massive star activating the supernova explosion. As per simulation results, capture rates on chromium isotopes have a major impact on controlling the lepton-to-baryon fraction of the stellar core during the late phases of evolution of massive stars. In this paper we calculate the electron capture rates on isotopes of chromium with mass range $42\leq A \leq 65$, including neutron-deficient and neutron-rich isotopes. For the calculation of weak rates in stellar matter, we used the pn-QRPA model with separable Gamow-Teller forces and took deformation of nucleus into consideration. A recent study proved this form of pn-QRPA to be the best for calculation of GT strength distributions amongst the pn-QRPA models. The stellar weak rates are calculated over a broad range of temperature $(0.01 \times 10^{9}-30 \times 10^{9} (K))$ and density $(10-10^{11}(g/cm^{3}))$ domain. We compare our electron capture rates with the pioneering calculation of Fuller, Fowler, and Newman (FFN) and with the large-scale shell model (LSSM) calculation. Our electron capture rates are enhanced compared to the FFN and shell model rates.

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arXiv2025

Gamma Ray Heating and Neutrino Cooling Rates due to Weak Interaction Processes on sd-shell Nuclei in Stellar Cores

Gamma ray heating and neutrino cooling rates, due to weak interaction processes, on $sd$-shell nuclei in stellar core are calculated using the proton neutron quasiparticle random phase approximation theory. The recent extensive experimental mass compilation of \citep{Wang12}, other improved model input parameters including nuclear quadrupole deformation \citep{Ram01}, \citep{Mol16} and physical constants are taken into account in the current calculation. The purpose of this work is two fold, one is to improve the earlier calculation of weak rates performed by \citep{Nabi99} using the same theory. We further compare our results with previous calculations. The selected $sd$-shell nuclei, considered in this work, are of special interest for the evolution of O-Ne-Mg core in 8-10 M$_\odot$ stars due to competitive gamma ray heating rates and cooling by URCA processes. The outcome of these competitions is to determine, whether the stars end up as a white dwarf \citep{Nabi08}, an electron-capture supernova \citep{Jones13} or Fe core-collapse supernova \citep{Suz16}. The selected $sd$-shell nuclei for calculation of associated weak-interaction rates include $^{20,23}$O, $^{20,23}$F, $^{20,23,24}$Ne, $^{20,23-25}$Na, and $^{23-25}$Mg. The cooling and heating rates are calculated for density range ($10 \leq ρ($\;g.cm$^{-3}) \leq $ 10$^{11}$) and temperature range ($0.01\times10^{9}$ $\leq$ $\;T(K)$ $\leq$ $30\times10^{9}$). The calculated gamma heating rates are orders of magnitude bigger than the shell model rates (except for $^{25}$Mg at low densities). At high temperatures the gamma heating rates are in reasonable agreement. The calculated cooling rates are up to an order of magnitude bigger for odd-A nuclei.

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arXiv2025

Expanded calculations of pn-QRPA electron capture rates on $^{55}$Co for presupernova and supernova physics

Due to its abundance and its relatively high capture rates, $^{55}$Co is one of the key nuclide that can control the dynamics of core collapse of a massive star. Previously we introduced our microscopic calculations of capture rates on $^{55}$Co using the proton-neutron quasi-particle random phase approximation (pn-QRPA) theory. Here we present for the first time an expanded calculation of the electron capture rates on $^{55}$Co on an extensive temperature-density scale. These type of scale is appropriate for interpolation purposes and of greater utility for simulation codes.

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arXiv2025

Investigation of Gamow Teller Transition Properties in 56-64Ni Isotopes Using QRPA Methods

Weak rates in nickel isotopes play an integral role in the dynamics of supernovae. Electron capture and $β$-decay of nickel isotopes, dictated by Gamow-Teller transitions, significantly alter the lepton fraction of the stellar matter. In this paper we calculate Gamow-Teller (GT) transitions for isotopes of nickel, $^{56-64}$Ni, using QRPA methods. The GT strength distributions were calculated using four different QRPA models. Our results are also compared with previous theoretical calculations and measured strength distributions wherever available. Our investigation concluded that amongst all RPA models, the pn-QRPA(C) model best described the measured GT distributions (including total GT strength and centroid placement). It is hoped that the current investigation of GT properties would prove handy and may lead to a better understanding of the presupernova evolution of massive stars.

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arXiv2025

Study of Gamow-Teller strength and associated weak-rates on odd-A nuclei in stellar matter

In a recent study by Cole et al., it was concluded that QRPA calculations show larger deviations and overestimate the total experimental Gamow-Teller (GT) strength. It was also concluded that QRPA calculated electron capture rates exhibit larger deviation than those derived from the measured GT strength distributions. The main purpose of this study is to probe the findings of the Cole et al. paper. This study gives useful information on the performance of QRPA-based nuclear models. As per simulation results, the capturing of electrons that occur on medium heavy isotopes have a significant role in decreasing the ratio of electron-to-baryon content of the stellar interior during the late stages of core evolution. We report the calculation of allowed charge-changing transitions strength for odd-A fp-shell nuclei (45Sc and 55Mn) by employing the deformed pn-QRPA approach. The computed GT transition strength is compared with previous theoretical calculations and measured data. For stellar applications the corresponding electron capture rates are computed and compared with rates using previously calculated and measured Gamow-Teller values. Our finding show that our calculated results are in decent accordance with measured data. At higher stellar temperature our calculated electron capture rates are larger than those calculated by Independent Particle Model (IPM) and shell model. It was further concluded that at low temperature and high density regions the positron emission weak-rates from 45Sc and 55Mn may be neglected in simulation codes.

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arXiv2025

Energy Rates Due to Weak Decay Rates of Vanadium Isotopes in Stellar Environment

The neutrino cooling and gamma heating rates are considered as an important input needed to study the final phases of the evolution of high-mass stars. The weak-interaction mediated processes, namely the $β$-decay and electron capture, significantly change the lepton to baryon ratio and accelerate the contraction of the core. The emission of resulting neutrinos/antineutrinos tends to cool the stellar core. On the other hand, gamma rays are produced because of electron capture and $β$-decay to excited states in daughter nuclei. These gamma rays heat the core and contribute to an increase of entropy which may cause convection to occur. In the present work, the weak-interaction heating and cooling rates on a chain of twenty-two isotopes of vanadium having mass in the range $43-64$ have been estimated using the proton-neutron quasiparticle random phase approximation theory. The rates have been computed for the temperature ranging from ($10^{7} - 3 \times 10^{10}$)\;K and for the density range ($10-10^{11}$)\;g/cm$^{3}$. Our calculated neutrino energy loss rates have also been compared with the previously reported rates calculated using other theoretical models. At high stellar temperatures, our rates are larger by 1-2 orders of magnitude as compared to previous results.

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arXiv2025

Neutrino cooling rates due to nickel isotopes for presupernova evolution of massive stars

Simulation studies indicate that weak interaction rates on nickel isotopes play a crucial role in determining the electron-to-baryon ratio within the stellar interior during the late stages of core evolution. (Anti)neutrinos produced through weak decay processes escape from stellar regions with densities below 10^11 g/cm^3, carrying away energy and thereby reducing the core entropy. In this work, we present a microscopic calculation of neutrino and antineutrino cooling rates resulting from weak interactions on nickel isotopes in the mass range 56 <= A <= 71. The calculations are performed using the deformed proton-neutron Quasiparticle Random Phase Approximation (pn-QRPA) model. Recent investigations into the Gamow-Teller (GT) strength distributions of nickel isotopes demonstrate that the deformed pn-QRPA model successfully reproduces experimental charge-changing transition data.

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arXiv2025

Ground-state nuclear properties of neutron-rich copper isotopes and lepton capture rates in stellar matter

This study consists of two separate investigations centered on neutron-rich isotopes of copper, utilizing two distinct nuclear models. In the first part, the nuclear ground-state properties of copper isotopes in the mass range 72 <= A <= 82 were analyzed using the relativistic mean field (RMF) model. Quadrupole moment-constrained RMF calculations were carried out with DD-ME2 and DD-PC1 density-dependent interactions to compute the ground-state binding energies, charge radii, proton and neutron radii, quadrupole moments, and deformation parameters for the 71-82Cu isotopes. The results show good agreement with the limited experimental data available and previous theoretical predictions. In addition, potential energy curves were evaluated to investigate the ground-state geometrical configurations of these isotopes. The second part of the study is devoted to calculating lepton capture rates under stellar conditions. While earlier works have provided allowed Gamow-Teller (GT) and unique first-forbidden (U1F) beta-decay rates for selected neutron-rich Cu isotopes in stellar environments, the corresponding lepton capture rates had not yet been computed. This paper presents, for the first time, those lepton capture rates.

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arXiv2025

Lepton capture rates due to isotopes of vanadium in astrophysical environment

Lepton (electron and positron) capture rates on iron-regime nuclei are an essential element for modeling the late stages in the evolution of massive stars that end as core-collapse and thermonuclear supernovae. Previous simulation studies suggest that lepton capture (LC) rates on isotopes of vanadium have a substantial effect in regulating the electron fraction (Ye) during the final evolutionary phases. The present work involves the calculation of LC rates for 22 isotopes of vanadium using the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. The considered mass range is from A = 43 to 64. The LC rates are computed over stellar densities ranging from 10^1 to 10^11 g/cm^3 and temperatures in the range 10^7 to 3 x 10^10 K. A comparison of our LC rates with those obtained using other models (IPM and LSSM) is also presented. Compared to other models, the pn-QRPA rates at high temperature (3 x 10^10 K) are larger by 1-2 orders of magnitude.

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arXiv2025

Nuclear structure properties and decay rates of molybdenum isotopes

Electron capture and beta-minus decay are the dominant decay processes during the late phases of the evolution of heavy stars. Previous simulation results show that weak rates on isotopes of Molybdenum (Mo) have a meaningful contribution during the development of phases of stars before they go supernova. The relative abundance, coupled with the stellar weak rates on Mo isotopes, may change the lepton-to-baryon content of the core material. Here, we report on the calculation of nuclear structure properties of Mo isotopes from mass number 82 to 138, employing the RMF model. Later, we calculate the weak decay rates of these isotopes using the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. In the first step, the ground-state nuclear properties of Mo isotopes such as binding energy per nucleon, neutron and proton separation energies, charge radii, total electric quadrupole moments, and the deformation parameter of electric quadrupole moments have been calculated using the density-dependent version of the RMF model with DD-PC1 and DD-ME2 functionals. The calculated electric quadrupole deformation parameters have been used in a deformed pn-QRPA calculation in the second phase of this work to calculate half-lives and weak decay rates for these Mo isotopes in stellar matter. We calculate the electron capture and beta-decay rates over an extensive range of temperature (0.01 x 10^9 K to 30 x 10^9 K) and density (10 to 10^11 g/cm^3). Our study can prove useful for simulation of presupernova evolution processes of stars.

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arXiv2025

Nuclear Structure Properties of even-even Chromium Isotopes and the E ect of Deformation on Calculated Electron Capture Cross Sections

In this study, we investigate the role of nuclear deformation on the calculated electron capture cross section (ECC) of even-even chromium (Cr) isotopes. We first determined the nuclear structure properties of these nuclei within the interacting boson model-1 (IBM-1). The energy spectra and E2 transition probabilities were calculated by fitting the parameters in the model formalism. The analysis of the potential energy surface was also performed to predict the geometric shape of the Cr nuclei by plotting their contour plot in the plane of (beta, gamma) deformation parameters. Later, we calculated the ECC within the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. In particular, we studied how the calculated ECC changed with different values of the nuclear deformation parameter. The calculated Gamow-Teller (GT) strength distributions were widely spread among the daughter states. The total GT strength decreased with increasing value of the beta parameter. The computed ECC values, however, increased with increasing beta values of the Cr isotopes.

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